As the use of plastic products is very widespread, reuse of the plastic waste represents a huge challenge. Plastic packing (e.g. plastic bags, plastic packing of ham, cheese, yoghurt, and other food products and consumer goods, and other plastic packing, plastic dishes) and other plastic waste (box pallets, garden furniture, buckets, plastic sledges, car bumpers, canisters, pipes, bobbins, computer cases, TV sets, plastic refrigerator details, etc.) form the most problematic and continuously growing type of waste, that according to common solutions can today be mainly landfilled, incinerated or used as filling material. Such solutions pollute the environment, are costly, and at the same time waste material that could be used as raw material for new applications.
Initial sorting of waste and subsequent recycling of single-type plastics into uniform mass, granules or new products are the generally grown solutions for recycling plastic. Recycling is performed based on one specific type of plastic, e.g. LDPE, HDPE, or PET, in the course of which the sorted plastic waste is washed, broken up, dried and granulated. The plastic granules produced based on the recovered single-type polymer can be used by the plastics industry as raw material for manufacturing new products. As sorting plastic waste by their types is, however, very costly and time-consuming, difficult to sort mixed plastic waste is mostly not recycled, and due to that mixed plastic waste is channelled to incineration or landfilling.
As far as known, no suitable solution has been found for recycling polymers of different types. When comparing polymer materials to other materials like glass and metals, the polymers of a plastic need longer processes to enable their recovery. The biggest problem is posed by the fact that polymers of different types are immiscible with each other because of their different molecular weights and long polymer chains. Heating the polymers is not sufficient for decomposing polymer molecules; therefore, the polymers to be recovered must often have identical compositions to achieve effective mixing. When plastics of different types are simultaneously melted together, they usually do not mix—like oil and water—and will lie in layers.
Because of such problems the unsorted waste of mixed plastics remains unused by the plastics industry; also sorting plastic waste from households and other consumers by their types is very costly or almost impossible. Standard plastics industries manufacturing hundred millions tons of plastic products to be used, are configured to work with virgin, or initial single-type plastic granules (LDPE, HDPE, PS, PP, PET, AB, composites, (PS/PP, PP/PE, PS/PC), HIPS, EPS, PA, POM, PC, etc.), and their technological production solutions are not capable of handling mixed and contaminated plastic waste.
The scientific base known up to now does not support effective solutions for mixing different and recovered polymers; the opinion that this cannot be achieved has become dominant.
Experiments attempting to recycle mixed plastic waste of different types are known from the state of the art. Such solutions, however, also involve sorting and/or adding of other materials during the recycling process, to facilitate better binding of the mixture obtained by recycling. For example, a solution involving recycling of different waste into granules is known from the international patent application WO2012009005. Wastewater and several other types of waste are added to plastic waste according to this solution. The material obtained using this solution is not homogeneous. International patent application WO0238276 describes a process and device for recycling plastic household waste, but the solution requires preliminary cleaning and sorting of the plastics.
The process described in U.S. Pat. No. 6,274,637B1 for producing a material mixture from mixed plastics, plastic waste or other unidentified or known plastics, and manufacturing products from it by mixing, breaking up, thermal processing, and moulding/cooling can be considered the closest known solution from the state of the art. According to this solution, pre-sorted plastic materials, other substances, and additives (fatty acids are used) are mixed together. The mixture of all components is thermally processed in the course of up to twelve-stage and up to 400° C. heating cycle, and the outcoming mass is either cooled or conveyed to product manufacturing. This solution uses either an extruder or injection moulding machine device. The fraction size of the material produced by recycling is 0.1 to 5 mm. The solution provided describes recycling of plastic waste of different types, including plastic waste of small and large volume weights, together with other materials (metal, wood, sawdust, paper, rubber, fibres) or unknown materials. It is generally known that plastics of different types mix poorly or not at all, in case of this solution yet other poorly miscible materials are added in the course of recycling. The material mixture obtained as a result is of poor quality, unstable, of non-uniform composition and low weatherproofness. Multiple-stage heating at high temperatures makes the process complicated, costly and time-consuming. This solution assumes that the recycled material containing plastics has been previously sorted. In addition to that fatty acids must be added during recycling that in turn further complicates the process. Only one embodiment has been provided as an example: a product manufactured from cable waste, and a mixture of PVC, PE and rubber granules. No other process parameters aside from temperature ranges have been specified for the solution provided, including, e.g. pressure, time or other conditions to be monitored during the process.
Considering the properties of the materials listed for the solution provided, and the incomplete process specification, such solution is not practicable according to the opinion of a person skilled in the art.
The biggest shortcoming of the prior art solutions is producing an extremely unstable mass by mixing and melting different plastics, that cannot be managed by the currently known plastic processing process, let alone enable a stable raw material to be achieved and finished products to be manufactured from it.